The proposed research is expected to provide information about the pathogenesis of Legionnaires' Disease, and to characterize various host responses to infection. This will be accomplished by developing a rodent model of pulmonary infection with the bacterium responsible for Legionnaires' Disease. Specific manipulations of the model will be designed to evaluate clinically relevant questions such as immunity to infection and the effect of immunosuppressant drugs on susceptibility to and progress of disease.